This invention relates to reaction injection molded polymer polyurethanes which are prepared using polyahls chain extenders.
Reaction injection molded polyurethanes are well-known in the art as described by F. Melvin Sweeney in Introduction to Reaction Injection Molding, Technomics, Inc., 1979. The use of reaction injection molding (RIM) of polyurethanes in the production of structural parts for automotive applications such as fenders, doors and body panels as well as in other applications such as computer housings, office equipment housings, sports equipment and the like is well-known.
In the practice of RIM processes to produce a molding having a compact surface skin, a mold is filled with a highly reactive, liquid starting component within a very short time by means of a high output, high pressure dosing apparatus after the components have been mixed in so-called positively controlled mixing heads. In such "one-shot" processes, the highly reactive starting materials which are generally a polyether or a polyester having a plurality of active hydrogen moieties, a polyisocyanate and a chain extender such as a diol or a polyamine as well as other conventional additives such as blowing agents, catalysts, fillers and the like, are delivered mechanically within a very short time (generally from 2 to 4 seconds) and mixed at the same time and introduced into the mold in which the mixture is cured to yield the finished product within a time (generally from 1 to 2 minutes) and thereby produce a polyurethane product. The polyurethane-forming compositions have been the material of choice for RIM applications due to their short reaction times and easy handling which thereby allows rapid cure and short cycle times. Unfortunately, such formulations often do not have sufficient temperature resistance to withstand paint curing conditions employed by the automotive industry without deformation. While such deficiencies arising from low temperature resistance of finished parts have been overcome to some extent by the use of various diamines as chain extenders instead of diols, such amines are often highly reactive thus leading to premature cure prior to the filling of the mold. In addition, even further increase in temperature resistance of the resulting RIM part is desired for many applications which could otherwise advantageously employ RIM structural parts.
In view of the foregoing deficiencies of conventional RIM formulations, it would be highly desirable to provide a formulation which can be introduced into the mold without significant premature curing and which yields a finished molded article capable of withstanding temperatures as high as 325.degree. F. while retaining original dimensions and physical properties.